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A dual band circularly polarized single-feed microstrip antenna for wireless communication systems is proposed here and its performance is tested in free space. This modified rectangular microstrip antenna having one protruded curved edge is simulated by using the IE3D simulation software. In between conducting patch and ground plane, designed antenna has two layers of glass epoxy FR-4 substrates separated by a thin layer of foam substrate. This designed antenna operates at two frequencies 3.10 GHz and 3.55 GHz and presents circularly polarized performance in far-field region. The measured impedance bandwidth of designed antenna is 26%(0.846 GHz) with respect to the central frequency 3.31 GHz. The axial ratio bandwidth at two frequencies 3.10 GHz and 3.55 GHz is close to 1.36% & 2.21% respectively. The measured E plane co and cross radiation patterns in entire impedance bandwidth are identical in shape and direction of maximum radiations is normal to patch geometry as the losses in cavity reduce as the quality factor of the cavity is decreased.